The present invention relates to the control of vehicles moving on a fixed guideway. For many years, the only application for this technology was to control long distance railroad traffic. More recently, however, the technology has been applied to the control of rapid transit vehicles which, by their nature, were restricted to dense urban areas. Even more recently, however, this technology has also been applied to the control of what is termed "personal rapid transit" or PRT, which technology can be applied to less dense areas than that required by the rapid transit systems.
In this field, two exclusive control philosophies have developed. The earlier control philosophy will, for purposes of this application, be termed "fixed block". In this philosophy, the vehicle guideway is divided into segments called blocks. Apparatus is arranged in each block, for detecting the presence of a vehicle in that block. This wayside apparatus may be coupled to wayside apparatus of one or more adjacent upstream blocks for the purposes of informing vehicles in such upstream blocks of the presence of a vehicle in a downstream block. In one specific application, for example, the block directly upstream of an occupied block is provided with a signal requiring an emergency stop. The next adjacent upstream block is provided with a signal requiring a stop, the next adjacent upstream block is provided with a signal calling for a low speed, and so on. In effect, an information communication arrangement is combined with distributed wayside data processing or computing. In such a system, the vehicle headway, that is, the distance between moving vehicles, is at least one block long, and may, in normal practice, be two or more blocks long. Since the apparatus required for this control philosophy is directly proportional to the number of blocks, economy dictates increasing block length. On the other hand, in order to increase system efficiency, that is, traffic moved per unit of time, decreasing block length is indicated. In the past, a compromise is arrived at fixing a particular block length. However, because of the control philosophy, minimum separation between vehicles is related to block length which is fixed and unchangeable.
In response to the known problems with this control philosophy, the prior art has also developed the "moving block". With this arrangement, each vehicle that is being controlled, transmits its location to a controlling authority, usually on a periodic basis. Thus, the controlling authority has available to it information as to the location and, perhaps speed, of all the vehicles being controlled. Under these circumstances, the controlling authority then provides signals to the vehicles, based upon downstream traffic conditions, allowing the vehicles to proceed at safe speeds, or on the other hand, requiring the vehicles to stop. In effect, a multiple communication arrangement coupled with centralized wayside data processing or computing. At first blush, this approach might appear to solve all the problems of the "fixed block" in that headway can apparently be reduced at will by merely increasing the rate at which information flows from the vehicles to the controlling authority and from the controlling authority to the vehicles. The difficulty encountered herein relates to the vast requirement for information transfer and, if the system is to be automatic, for computing power.
Another difficulty with both prior art solutions is lack of flexiblity to respond to changed conditions. The fixed block is extremely limited in increasing traffic flow above a fixed amount since there is a minimum headway which can only be decreased by reducing block length and block length can only be reduced at extreme expense--it requires a complete replacement of apparatus. The moving block is not as limited since decreases in headway can be achieved by multiplying computing power and information transmission rates. However, these capabilities can only be increased at enormous costs, especially since the computing and information transfer control safety which requires fail safe procedures.
It is therefore one object of the present invention to provide a control philosophy which blends the advantages of both the moving block and the fixed block approach while, at the same time, avoids the disadvantages of each. It is another object of the present invention to provide a control system in which economic advantages of the fixed block approach may be retained, while, at the same time, approaching the flexibility of the moving block control system. Another object of the invention is to simplify the apparatus associated with each block so block length can be reduced without an extreme economic penalty.